This application claims the priority of German patent document 196 47 605.4, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an exhaust turbocharger for internal combustion engines.
Exhaust turbochargers of the generic type are known. As a centrifugal-compressor map stabilizing measure, along the contour of the compressor impeller, approximately in the first quarter of the length of the impeller, parallel to the intake duct, a bypass is provided within the compressor housing in the form of an annular gap. The bypass is composed of a radial inlet groove located upstream from the compressor impeller, a radial contour groove located downstream from the inlet edge of the compressor impeller, and an annular chamber connecting these two grooves. The annular gap located parallel to the intake channel (and hence parallel to the inlet to the impeller itself) produces bypass mass flows which, in the area of the surge line, (that is, in the area of minimal volume flow delivery) and in the area of the plug limit (the area of maximum volume flow delivery), permit a shift toward smaller and/or larger volume flows by comparison with machines of the same design without a bypass.
The advantageous and desirable centrifugal-compressor map expansion thus achieved is attained at the expense of disadvantages in efficiency that are reflected in a disturbing higher noise level. For this reason, the object of the invention is to avoid these disadvantages while retaining the desired centrifugal-compressor map expansion.
According to the invention, this is accomplished by providing an exhaust turbocharger with a bypass which stabilizes the centrifugal compressor map. The bypass has a variable effective cross section, which is preferably set to an optimum width only in those areas of the centrifugal-compressor map field of the compressor that are near the surge line and/or the plug limit of the compressor. In other words, the bypass has an optimized cross section, but can be closed in between.
For this purpose, it may be advantageous within the scope of the invention to provide the inlet groove and/or the contour groove with variable widths, preferably to make them closable.
As a sealing element, an annular slide can be provided, which can be made in several parts, so that both grooves can be covered by telescopic adjustment.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.